http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56981
Bug #: 56981
Summary: Slow I/O: Unformatted 5x slower, large sys component;
formatted slow as well
Classification: Unclassified
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: bur...@gcc.gnu.org
CC: j...@gcc.gnu.org, jvdeli...@gcc.gnu.org
Found at
https://groups.google.com/forum/?fromgroups=#!topic/comp.lang.fortran/ORw0Y2k2CI4
The following examples are taken from Robert Corbett.
The large amount spend in system for unformatted I/O is surprising, compared
with other compilers. But in general, unformatted I/O is much slower.
(Formatted I/O is slow as well.)
---- Timing in sec ------------------------------------------------
Unformatted Formatted
real / user real / user Compiler
----------- ----------- -----------------------------------------
1.467/0.448 3.205/2.780 GCC 4.8.0 (-Ofast, 20130308, Rev. 196547)
0.309/0.308 1.297/1.296 g95 4.0.3 (g95 0.93!) Aug 17 2010 (-O3)
0.199/0.188 0.562/0.548 Sun Fortran 95 8.3 Linux_i386 2007/05/03
0.177/0.172 0.904/0.900 PathScale 3.2.99
0.177/0.176 2.201/2.200 NAGWare Fortran 5.1
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
0.578/0.205 1.229/1.121 GCC 4.9 (trunk, -Ofast)
0.115/0.113 0.517/0.513 g95 4.0.3 (g95 0.94!) Dec 17 2012
0.130/0.129 0.522/0.517 PathScale EKOPath 4.9.0
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1.035/0.524 3.014/2.928 GCC 4.7.2 20120920 (Cray Inc.)
0.194/0.184 0.634/0.632 Cray Fortran : Version 8.1.6
0.372/0.260 0.703/0.564 Intel 64, Version 13.1.1.163
0.437/0.432 0.938/0.932 pgf90 12.10-0
-------------------------------------------------------------------
PROGRAM MAIN
REAL X
OPEN (10, FILE='/dev/null', FORM='FORMATTED')
X = 0.0
DO 10 I = 1, 1000000
WRITE (10, '(E13.7)') X
X = X + 1.0
10 CONTINUE
END
-------------------------------------------------------------------
PROGRAM MAIN
REAL X
OPEN (10, FILE='/dev/null', FORM='UNFORMATTED')
X = 0.0
DO 10 I = 1, 1000000
WRITE (10) X
X = X + 1.0
10 CONTINUE
END
